anonymous question

The topic of direct military conflict was best explored by Vladimir Zolotorev, whom I have mentioned repeatedly, in the series of articles “Insurance Company ‘Sonechko’ versus the Tsardom of Muscovy”.
Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Most likely, this volume of material will be sufficient for you to address both the question you asked and several related ones.

But I will still make a small clarification regarding one of the models of creeping expansion you mentioned. Buying up all the land is very unrealistic, because the less unsold land remains, the more expensive it becomes, and the happy sellers of land receive more and more resources, which they can invest in assets that seem more profitable to them than the land they have just sold.

At the same time, the fact that a certain NAP violator is a landowner does not protect them in any way. They violated it — a conflict arose, now they either pay a penalty or they are fought against. In a state, the law may protect a NAP violator, but for ancaps, dealing with such problems is much simpler.